Polymers of styrene are common and valuable plastics that may be used in the production of items from electronics casing to toys to disposable plates and cups. The chemical formula of styrene monomer is C6H5C2H3, and its structure includes a benzene ring with an attached ethylene group. Styrene is generally produced by dehydrogenation of ethylbenzene. Ethylbenzene has the chemical formula of C6H5C2H5, and its structure includes a benzene ring with an attached ethyl group.
Ethylbenzene dehydrogenation takes place in a dehydrogenation reactor system, which may include one or more dehydrogenation reaction chambers and downstream processing equipment. Superheated steam and ethylbenzene enter the reaction chamber(s) as an input steam where a dehydrogenation catalyst catalyzes the conversion of ethylbenzene to styrene. The mechanism for the dehydrogenation reaction involves the loss of two hydrogen atoms from the ethyl group to form a carbon-carbon double bond. Thus, the chemicals exiting the reaction chamber(s) generally include styrene, hydrogen gas, and steam, as well as unreacted ethylbenzene and other compounds, which may be referred to as styrene offgas.
Occasionally, it may be desirable to subject the dehydrogenation reactor system to a turnaround, also referred to as a shutdown, such as to clean, repair, replace catalyst or otherwise maintain the dehydrogenation reactor system. Generally, a shutdown procedure for a dehydrogenation reactor system includes cooling down the dehydrogenation reaction chambers under a steam-only purge.
Catalyst agglomeration may increase the length of time that it takes to complete a turnaround. Catalyst agglomeration may include the formation clumped catalyst extrudite beds within the dehydrogenation reactor system, which may be fused with potassium. Catalyst agglomeration may be at least in-part caused by potassium migration and long run times of the dehydrogenation reactor system. Without wishing to be bound by theory, potassium is a major catalyst component and may form KOH (potassium hydroxide) with steam at elevated temperatures. KOH has a significant vapor pressure and low melting point, allowing KOH to become mobile at reaction conditions. High potassium content and long run lengths with steam dilution may increase the severity of catalyst agglomeration in dehydrogenation reactor systems.